Abstract: According to the result of isotope tracer measurement and two-year original data of measure weir, osmometer and piezometer, taking advantage of the software package of eo6menu inversion calculation, applying saturation-non-saturation method of finite difference integration, the thesis carries out the inversion calculation of tridementional vadose field in Xiao shan hydropower station under four different conditions, and obtain the optimized solution of inversion calculation . The solution indicates that the vadose water of the measuring weir behind Xiao shan hydropower station dam mainly comes from basalt and the unconformity of basalt and andesite . The solution provides the disposal of the dam with a lot of fixed-amount basis.